Sulphur dioxide: why does wine contain sulphites?

Sulphur dioxide is one of the most talked about topics in the wine world. Around it revolve myths, urban legends, rubbish, weird ideas and so on and so forth. That is why today I decided to write this article where I tell you about 10 truths of the dreaded SO2 and especially on the why wine contains sulphites. 🤓 😎

1) Sulphur dioxide and sulphites: what are they?

SO2 is a gas with a characteristic burning matchstick smell that is formed by the combustion of sulphur. Sulphites are therefore an additive and as such must be indicated on the label.

2) Sulphur dioxide: does it have side effects?

SO2 has several side effects and is therefore classified by European regulations as one of the 14 substances used that can cause allergies and/or intolerances. So when you hear some winemaker say that this is all bullshit, know that the CERTIFIED side effects are:

• is irritating;
• tastes unpleasant;
• can cause headaches (at very high doses).
• asthma or breathing difficulties.

Obviously, these are side effects that assume a hypersensitivity to SO2. I had already specified this, but it did not seem clear enough. However, this is why the law in wine allows very limited use of it. However, until now no equally good substitute has been found despite numerous attempts in the physical and chemical fields, and so it continues to be used, trying to moderate its use as much as possible.

So many foods have sulphites added to them, for example to improve preservation, so it should be compulsory to write the actual amount present on the label even for foods other than wine. It is understood that people who are not hypersensitive to sulphites are unlikely to have side effects unless they have consumed a great deal of sulphites from various food sources throughout the day (wine should be the tip of the iceberg!).

3) Sulphur dioxide: what is it used for?

1. Sulphur dioxide serves mainly as a selective antiseptic against microorganisms in the must. In practice, it serves to inhibit the development of undesirable strains (which can trigger undesirable spontaneous fermentations) by promoting the preservation of the right strains. When used at a low concentration (5-30 g/hl) kills many harmful microorganisms without damaging the saccharomyces. When used at high doses (130-180 g/hl), it irreparably damages saccharomyces, rendering the must mute, i.e. infermentescible. Its effectiveness depends on its concentration, the ambient temperature, the acidity and composition of the must, and finally the type and stage of the micro-organism (yeasts are more resistant than bacteria, and the more inert the micro-organisms, the better the effectiveness of SO2).
2. Sulphur dioxide serves to solubilise colouring substances and polyphenols in general causing greater colour intensity and vibrancy. An overdose, however, causes the opposite, discolouring action!
3. Sulphur dioxide serves to acidify the wort directly or indirectly. In the latter case, we have an inhibition of lactic bacteria and a reduction in malolactic fermentation as lactic acid is weaker than malic acid.
4. Sulphur dioxide serves to defecate must as the increased acidity facilitates the flocculation of negatively charged colloids.
5. Sulphur dioxide serves to prevent oxidation thanks to its reducing properties (it is easy for it to oxidise to sulphate... ah the oxidation reactions I studied in chemistry at university... see what they were for?). The peroxides that arise from polyphenols are the first to benefit from its antioxidant action. Moreover, this action destroys and inactivates the oxidases responsible for the oxidasic case (I advise you to brush up: Wine alterations, defects and diseases).

4) Sulphur dioxide: in what form is it used?

Sulphur dioxide can be used in various forms:

• GASEOUS STATE: in this case the treatment  - which is based on the combustion of discs or fuses of sulphur suspended inside closed vessels - is only used to sterilise wooden wine vessels.
• LIQUID STATUStreatment is carried out with cylinders from which the SO2 comes out with a nozzle.
• SOLID STATEIn this case, the treatment is done with sodium sulphite, sodium bisulphite, sodium metabisulphite and potassium salts. Small producers generally prefer this method.

5) Sulphur dioxide: how do we find it in wine or must?

SO2 is present in musts or wines:

• Sulphur dioxide in free formwine is a hydroalcoholic solution and in this type of environment the SO2 forms hydrates that dissociate, releasing H+ ions, forming - it is thought - sulphurous acid. Consequently we obtain bisulphites, metasulphites... and where the pH>5 also sulphites. The antibacterial function is maximum.
• Sulphur dioxide in bound formSO2 - and its derivatives - combine with molecules with an aldehyde, carbonyl or ketone function (acetic adelaide, sugars, pyruvic acid and α-ketoglutaric acid) and, to a lesser extent, with proteins and polyphenols. Of all these combinations, only the one between sulphur dioxide and acetic aldehyde is stable and definitive, thus guaranteeing an antibacterial function.

6) Andride solforosa: in che fase del processo produttivo del vino viene utilizzata?

In cantina durante il processo di produzione del vino l’anidride solforosa può essere utilizzata in più fasi, dal trattamento delle uve alla pulizia dei vasi vinari, dalla solfitazione del mosto alla sofiltazione del vino. Tuttavia il momento migliore per aggiungere anidride solforosa è nella fase di ammostamento o comunque prima che abbia inizio la fase di fermentazione.

7) Andride solforosa: quando è necessario alzare le dosi?

Sono sicura che almeno una volta qualcuno ti ha detto “il vino si fa in vigna”. Ecco, diciamo che per quanto riguarda il contenuto di anidride solforosa è sicuramente vero! Se utilizzi uve danneggiate o non ottimali dal punto di vista del rapporto tra acidità e concentrazione zuccherina magari con un PH basso serve alzare la dose di anidride solforosa. Probabilmente hai notato che con vini bianchi di bassa qualità è più facile che ti viene mal di testa… questo accade perchè per la vinificazione in bianco è comunque necessaria una dose maggiore di anidride solforosa e tra le cose ostacola anche la fermentazione malolattica (come ti ho spiegato al punto 4) e se le uve sono alterate e se ne deve aggiungere di più… la frittata è fatta!

8) Andride solforosa: qual è la dose massima consentita e cosa dice la legge?

• 150 mg/l per i vini rossi o liquorosi con zuccheri inferiori a 5 mg/l, tetto che può essere alzato fino  a 200 mg/l nel caso di vini rossi o liquorosi con quantità di zuccheri (espressi dalla somma di glucosio e fruttosio) superiore a 5 mg/l;
• 185 mg/l per i vini spumanti di qualità, tetto che può essere alzato fino a 235 mg/l per tutti gli altri vini spumanti;
• 200 mg/l per i vini bianchi e rosati con zuccheri inferiori a 5 mg/l, tetto che può essere alzato a 250 mg/l nel caso di vini bianchi o rosati con quantità di zuccheri (espressi dalla somma di glucosio e fruttosio) superiore a 5 mg/l.

• E 200-203: acido sorbico che può essere aggiunto da solo o in combinazione e il livello massimo è applicabile alla somma, espresso in acido libero;
• E 220-228: anidride solforosa, solfiti i cui livelli massimi sono espressi come SO2 e si riferiscono alla quantità totale, disponibile da tutte le fonti; non è presa in considerazione la SO2 di tenore non superiore a 10 mg/kg o 10 mg/l.

9) Andride solforosa: cosa cambia nei vini biologici, biodinamici o naturali?

Come puoi ritrovare nel Regolamento Europeo di Esecuzione 203/2012.

10) Andride solforosa: cosa sono i vini senza solfiti aggiunti?

Spero come sempre di esserti stata utile! Se vuoi approfondire l’argomento o se hai qualcosa da aggiungere ti invito a scorrere la pagina e a lasciarmi un commento.

Cheers 🍷

Chiara

All my notes on wine and food in one book.